1. Field of the Invention
The present invention relates to a fuel injection control system for use with an engine, and more particularly to an improvement in the electric arrangement of an electronic fuel injection control system.
2. Prior Art
The rate at which fuel is supplied to an engine is required to be controlled according to the operating conditions of the engine. In recent years, such fuel supply control has been performed by an electronic control system using a microcomputer.
FIG. 5 of the accompanying drawings illustrates one conventional electronic fuel injection control system for an engine.
In FIG. 5, the electronic fuel injection control system includes a central processing unit (CPU) 11, a read-only memory (ROM) 12, a random-access memory (13), an input port 14 for receiving signals from various sensors on the engine, an output port 15 for generating signals to operate various actuators, a driver circuit 16 for operating fuel injection valves, and a data bus 17 for transferring data between the CPU 11, the ROM 12, the RAM 13, the input port 14, and the output port 15.
The ROM 12 stores a program for processing logics and an operation sequence to be executed by the CPU 11 and data for controlling processing operations. The RAM 13 serves to store input and output data and processed data. The input port 14 is supplied with various sensor signal data DT such as engine vacuum PB, engine speed Ne, coolant temperature Tw, and throttle opening .theta.th. These data items are converted by an A/D converter (not shown) to corresponding digital signals that are supplied to the CPU 11 for processing.
The output port 15 produces pulse-duration signals and on-off signals required to operate various actutators (not shown). For a four-cylinder engine, for example, the output port 15 has, in its area related to the fuel injection system, four counters 151 through 154 corresponding to the four engine cylinders, and an additional asynchronous counter 150. The counters 151 through 154 successively operate corresponding units 161 through 164 of the fuel injection valve driver circuit 16. The counter 150 however operates all of the units 161 through 164 simultaneously. The units 161 through 164 of the driver circuit 16 serve as driver units for respective fuel injection valves (not shown) on the engine cylinders. The driver units 161 through 164 include respective power amplifiers (not shown) for generating electric power required to actuate the fuel injection valves in response to output signals from the counters 151 through 154 or an output signal from the counter 150.
Operation of the conventional control system shown in FIG. 5 is as follows:
A certain crank angle during rotation of the engine, for example, the angle of 90 degrees prior to an intake stroke corresponds to a top dead center. This angle position is detected by a top-dead-center sensor to produce a top-dead-center signal (TDC signal) S1, based on which the CPU 11 starts operating. More specifically, the CPU 11 is responsive to the first TDC signal for computing the amount of fuel to be injected into the #1 cylinder, i.e., the time for which the #1 fuel injection valve is to be opened. Similarly, the CPU 11 is responsive to the second TDC signal for computing the amount of fuel to be injected into the #3 cylinder, i.e., the time for which the #3 fuel injection valve is to be opened. In response to the third and fourth TDC signals, the CPU 11 computes the times for which the respective #4 and #2 fuel injection valves are to be opened to inject fuel into the #4 and #2 cylinders. The computed data items are delivered over the data bus 17 into the counters 151 through 154, respectively. The driver units 161 through 164 are responsive to these data items from the counters 151 through 154 for energizing solenoids (not shown) to open the fuel injection valves, respectively, for the computed times.
In addition to the above normal fuel injection timing, there is generated additional fuel injection timing by an interrupt caused by a timer cycle signal S2 that is produced by a timer operating out of synchronism with the operation cycle of the engine cylinders, under engine operating conditions requiring extra fuel such as during acceleration. More specifically, when an accelerating condition is detected on the basis of the timer cycle signal S2, the CPU 11 computes a time for which the fuel injection valves are to be opened in response to the timer cycle signal S2. Since the computed data does not have normal fuel injection timing, it is stored in the asynchronous counter 150. The asynchronous counter 150 energizes the driver units 161 through 164 simultaneously to open all of the fuel injection valves at the same time. The simultaneously injected fuel is consumed successively in the cylinders according to their strokes.
The conventional fuel injection control system as described above requires an extra counter in addition to those associated with the engine cylinders in order to operate the fuel injection valves to meet all engine operating conditions. This additional counter, which counts up to several binary positions in microseconds, makes the control system complex and costly.